Experimental Study on the Electrical Insulation Characteristics of R124

The insulation design of superconducting power equipment requires liquid dielectric with excellent electrical and thermal characteristics at cryogenic temperatures. Many liquid dielectrics have been used for cooling the superconducting materials, a potential choice being chlorotetrafluoroethane (R124), due to its good thermal conductivity. However, its electrical characteristics at low temperatures are yet to be investigated. In this paper, devices for measuring the volume resistivity and electrical intensity of R124 are designed and the prototypes are built. The changes in the volume resistivity and breakdown with respect to the parameters such as temperature and electric field are measured. It is observed that at low temperatures and with low strength electric fields, the volume resistivity of the R124 decreases rapidly with increase in the temperature. Conversely, its value increases with the increase of electric field strength. Also, it is observed that the breakdown field strength increases with the decrease of temperature. However, when R124 breaks down at high voltages, carbon deposition takes place, and thus, it cannot be used for cryogenic liquid insulation.